In a charged particle beam apparatus including an electron microscope such as a scanning electron microscope (SEM) and a transmission electron microscope (TEM), a lens is used which uses an electric field or a magnetic field for converging a charged particle beam. In the electric-field or magnetic-field lens, various types of aberrations occur inevitably. Therefore, even if the charged particle beam is tried to be narrowed by increasing a reduction rate, a spot diameter cannot be reduced in a case where the aberration is large, and observation of a microstructure and improvement of a dimension measurement accuracy and precision cannot be achieved.
In a charged particle beam apparatus, introduction of an aberration corrector is underway for improving resolution. This aberration corrector is constituted by multipole lenses provided in multiple stages, and removes an aberration by generating an electric field or a magnetic field in the multipole lenses. There is a plurality of types of aberrations, and appropriate setting of a multipole field is required in accordance with the types of aberrations.
Regarding the aberration corrector, there is one using four stages of 12-pole lenses, as disclosed in the following Non Patent Literature 1, for example. In the aberration corrector of Non Patent Literature 1, an adjustment method of a multipole field in accordance with types of aberrations is described as an aberration correction method.
The relationship between an aberration and a correction amount is disclosed in Non Patent Literature 2 or Patent Literature 1. Here, a relationship of the aberration and a combination of the multipole fields is derived by calculation under an ideal condition. Moreover, in Patent Literature 1, a technique is also disclosed which measures the aberration in the aberration corrector and corrects it. This technique acquires beam profile data from a plurality of images acquired while a focus is varied, obtains the aberration amounts of various types of geometric aberrations based on the acquired beam profile data, determines the correction amount to be input to the aberration corrector in accordance with the obtained aberration amounts, and removes the various types of aberrations.
The measurement of these aberrations, however, has to be performed by using a state in which a beam is in focus on a sample or a state in which the beam is slightly out of focus with respect to the state where the beam is in focus, as a reference. Maintaining the state in which the beam is in focus is easy to break because of effects of the aberration, and adjustment is required in a stage before a state in which the aberration measurement is possible. In this adjustment, processes have to be repeated, and adjustment time is a problem. Moreover, in these measurements, when only a specific element such as one kind of multipole field in one stage is made larger, the focus state cannot be maintained and therefore the measurement for every element is difficult. Because those measurements are difficult, the method of Non Patent Literature 2 has been considered.
A case is considered in which, in determination of a relationship between an aberration and the correction amount in advance, correction is made considering a deviation from an ideal state such as a mechanical positional deviation of a multipole in a corrector. In this case, when the aberration correction is made, an additionally generated aberration (a parasitic aberration) associated with the correction is further generated and has to be suppressed. In order to suppress this parasitic aberration, an auxiliary multipole field is excited in addition to a multipole field for a main purpose. Thus, when more sophisticated adjustment is considered, the relationship between the aberration and the correction amount requires a measurement of a combination of auxiliary multipole fields, in addition to a measurement of a relationship between an ideal multipole field and the correction amount, and a time required for that measurement is a problem. In addition, because the aberration amount depends on an electron optical condition, it is necessary to examine the relationship between the aberration and the correction amount for every electron optical condition. Thus, it takes a time corresponding to the number of the conditions.
Furthermore, in the aforementioned measurement of the relationship between the aberration and the correction amount, there is a disadvantage that, in a case where the parasitic aberration is large, a beam is out of a measurement range and the measurement cannot be performed. In order to avoid this, the measurement has to be repeated in fine steps, and the procedure becomes complicated.